The present invention relates to a magnetic recording device, and more particularly to differential type magnetoresistive device suitable for use in a reproducing magnetic head.
A differential type device (namely, a differential device) has been fabricated for a barber-pole type magnetoresistive device which is disclosed in Japanese patent application (unexamined publication Nos. 51-124410 and 51-124411), and for a shunt-bias type magnetoresistive device which is disclosed in Japanese patent application (unexamined publication No. 53-25645). In both the differential magnetoresistive device of the barber-pole type and the differential magnetoresistive device of the shunt-bias type, a shunt film made of Ti, Mo, etc. is formed on part or the whole of a thin magnetoresistive film made of permalloy, to shunt a current and to apply a magnetic field generated thereby to the magnetoresistive film. Here, there arises a problem that an output based upon the magnetoresistive effect is reduced by an amount corresponding to a current which flows through the shunt film.
Now, explanation will be made of a differential magnetoresistive device of the shunt-bias type, by way of example. FIG. 1 is a perspective view showing a differential magnetoresistive device of the shunt-bias type, and FIG. 2 is a sectional view taken along the line II--II of FIG. 1. Referring to FIGS. 1 and 2, a high-permeability magnetic film (for example, a permalloy film) 4 which acts as a magnetoresistive element, is formed on a substate 2, and a shunt film 6 made of a metal (for example, titanium or molybdenum) is formed on the permalloy film 4. Further, three parallel electrodes 8, 10 and 12 are formed on the shunt film 6. When a current I is caused to flow from each of the electrodes 8 and 12 to the electrode 10, the current I is divided into a current I.sub.1 flowing through the permalloy film 4 and a current I.sub.2 flowing through the shunt film 6. That is, I=I.sub.1 +I.sub.2. The current I.sub.2 forms a bias magnetic field for the permalloy film 4. However, the output of the device due to the magnetoresistive effect is reduced by an amount corresponding to the current I.sub.2 which flows through the shunt film 6.
Meanwhile, it has not been studied to form a differential magnetoresistive device of the soft-film-bias type. Here, "soft-film" means a film of soft magnetic material. In a conventional soft-film-bias type magnetoresistive device, there arises a problem that the waveform of an output signal from the device is deficient in symmetry, because a curve indicating the relation between the output voltage of the device and the alternating magnetic field applied to the device is not linear as will be explained later. Thus, the conventional soft-film-bias type magnetoresistive device has a drawback that the output thereof cannot be made large.